1. Field of the Invention
This invention relates to a positioning structure for a brake force supplier for use in an image forming apparatus, such as a copying machine, a facsimile machine, a printer, and a compound machine having combined functions of these machines, which comprises a main base frame, an upper frame openably mounted on the main base frame, and the brake force supplier for applying a brake force to the upper frame during a closing operation thereof.
2. Description of the Background Art
There has been known an image forming apparatus shown in FIG. 10 having a frame structure 200 constructed in the following manner. The frame structure 200 has a main base frame 210 internally provided with various parts such as an imaging unit including a photoreceptor, and an upper frame 220 on which an operating unit including ten key switches and a start button is arranged. In such conventional image forming apparatus having the above frame structure 200, a shaft 221 provided at the rear end of the upper frame 220 is fittingly inserted in bearing portions 211 (only one bearing portion is shown in FIG. 10) provided at the upper rear end of the main base frame 210 to render the upper frame 220 openable (rotatable) with respect to the main base frame 210.
The upper frame 220 is further provided with a pivotal movement transmitter (gear) 222 which is pivotally movable about an axis of the shaft 221 on the inside of the main base frame 210 in association with a rotation (opening/closing) of the upper frame 220. On the outer surface of a side wall of the main base frame 210, there is mounted a brake force supplier 230 in the form such as a gear damper and a torque limiter via positioning pins 212 and 213 that are projected on the side wall of the main base frame 210.
The brake force supplier 230 includes a driven gear 231. The driven gear 231 is driven in accordance with a rotation of the gear 222 via idle gears 241 and 242 that are integrally mounted on a common shaft 240.
With the above image forming apparatus, an operator sets the apparatus in an opened state by pivotally moving the upper frame 220 upward to perform a certain operation such as removal of a jammed sheet. When the operator is on the way of setting the apparatus in a closed state after the certain operation, the brake force supplier 230 applies a certain brake force to the upper frame 220 to reduce the closing speed of the upper frame 220. With this arrangement, there has been eliminated a possibility that a great impact force generates when the upper frame 220 comes into contact with the main base frame 210 at a final stage of closing.
The above image forming apparatus provided with the brake force supplier has recently suffered from the following problem. Specifically, the apparatus of recent model is loaded with an automatic document-feeder unit of a relatively heavy weight on the upper frame 220 to stack a number of original documents and to automatically feed the documents one by one. Accordingly, the total weight of the upper frame side becomes fairly heavy, causing that the conventional brake force supplier 230 cannot apply a brake force great enough to reduce the closing speed of the upper frame 220 to a desirable level.
To desirably reduce the closing speed of the upper frame 220 to cope with the heavy weight of the upper frame side, there has been proposed an idea of mounting a brake force supplier having a greater brake force. However, to meet a change in the brake force, the dimensions of the brake force supplier need changes (e.g., diameter of the main body or a number of gear teeth of the drive gear), and these changes in some cases require a change in a pitch of mounting holes formed in the opposite ends of the brake force supplier to receive the positioning pins 212 and 213. Accordingly, in mounting a brake force supplier having a greater brake force in place of the brake force supplier 230, the position of the pins 212 and 213 need to be adjusted in accordance with the pitch of the mounting holes of the newly mounted brake force supplier.